1. Field of the Invention
The present invention provides an enhanced rigid face seal for roller cone rock bits. More particularly, the seal arrangement of the present invention allows for enhanced face seal lubrication.
2. Description of the Related Art
In the field of rolling cutter rock drill bits, it is desirable to include dynamic sealing systems that will generally prevent the loss of lubricant from the bearing system as well as the entry of abrasive laden drilling fluid into the bearing system from outside the bit.
There are two basic types of sealing systems commonly used in rolling cutter drill bits. In most drill bits, an elastomeric compression type sealing system is used to seal the bearing system. These bits are believed to perform adequately in most drilling applications. For rock bits used in very severe bit applications, however, elastomeric seals are known to have operating limitations when used to provide the dynamic seal around the bearing system.
Mechanical rigid face seals have generally become widely used as the seal of choice for dynamically sealing the bearing systems in rock bits used in severe drilling environments. These seals are typically manufactured from materials that tolerate the thermal, chemical and mechanical attack of severe drilling environments. The rigid face seals are generally believed to provide a higher level of reliability in rock bits as compared to elastomer seals.
A typical prior art mechanical rigid face seal for rock bits is shown in FIG. 1 as including a pair of seal rings 50, 60 having opposing faces 52, 62. The faces 52, 62 have opposing sealing surfaces 54, 64 that form a dynamic sealing interface 90. As the sealing surfaces 54, 64 rotate relative to each other, they are typically urged together at a controlled force by one or more energizers (not shown), as disclosed for instance in U.S. Pat. Nos. 5,040,624, 4,838,365, 3,761,145 and 6,176,330, each of which is hereby incorporated herein by reference in its entirety. Although generally more expensive than elastomer seals, mechanical face seals are believed to better withstand the typically highly abrasive environment of rock bit drilling, assuring a level of performance in rock drilling bits which is believed to justify their higher cost.
Still referring to FIG. 1, one of the seal rings 50, 60 of the typical conventional mechanical rigid face seal design for use in rotary rock bits is formed with a gradually tapered shape, or spherical radius, 86 adjacent to and on the lubricant side of the sealing interface 90. This seal design creates a diverging geometry. As abrasives wear the outer periphery of the engaged sealing surfaces 54, 64 of the faces 52, 62, the diverging geometry facilitates inward movement of the engaged sealing surfaces 54, 64 (also known as the sealing band) across the faces 52, 62. During the life-span of the bit, the sealing surfaces 54, 64 and sealing interface 90 are thus known to migrate across the opposing faces 52, 62 from the outer diameter OD toward the inner diameter ID of the seal rings 50, 60. The spherical radius 86 must be gradual enough to allow the migrating sealing surfaces 54, 64 to maintain their approximate initial widths and sufficient contact with one another. At the same time, it is important to maintain a sufficient film of lubricant between the sealing surfaces (e.g. 54, 64) of the seal faces. If the film becomes too thin, frictional contact between the sealing faces can generate undesirable heat and high torque on the seal faces. Excess frictional heat can damage and ultimately disable components used with the rigid rings, such as elastomer energizers and ring positioners, and bearing system components. High torque can also have undesirable consequences. For instance, if elastomer energizers are transmitting the torque, they may slip. A small amount of slippage can cause excessive wear on the elastomer energizers, leading to an early failure. For another example, when coil spring energizers, such as shown in U.S Pat. No. 4,838,365, are transmitting the torques, it is possible, under some circumstances, for the coil spring energizers to fail. When the operating torques become too high, the shear forces on the coil springs can cause them to yield. Once any one of the springs yield, the seal assembly loses its ability to move in response to volume changes in the lubricant near the seal, leading to rapid seal failure.
Referring again to FIG. 1, in the conventional seal design, the lubricant passes through the minute space 88 formed between the seal faces 52, 62 by the gradually tapered shape, or spherical radius, 86. In an exemplary prior art design, this space is approximately 0.004 inches at its open end and decreases along the tapered face 52 to virtually nothing. The spherical radius on one ring of the conventional seal face geometry thus provides for both lubrication of the sealing surfaces, and an area for the sealing band to migrate across as axial face wear occurs. Under this seal design, if the spherical radius 86 is sized incorrectly, the sealing interface 90 cannot be maintained as the seal faces 52, 62 wear, and the seal will prematurely fail.
In considering existing technology for roller cone rock bits, there remains a need for a rigid face seal arrangement that provides enhanced lubrication to the sealing interface, reduces seal face heat checking, is cost-effective, relatively simple to manufacture, durable and/or can be used with existing bit components, or a combination thereof.
The invention is useful in rolling cutter rock drill bits having a bit body with at least one depending leg, a bearing shaft formed on the leg(s), a rolling cutter rotatably mounted upon the bearing shaft, a bearing cavity formed in the rolling cutter and a lubricant disposed within the bearing cavity. In accordance with certain embodiments, the invention includes a pair of energized rigid face seals disposed between each leg and the rolling cutter and having opposing seal faces. The seal faces include opposing engagable sealing surfaces, which are constructed at least partially of generally wear-resistant material. A xe2x80x9cdistinctxe2x80x9d gap is formed between at least part of the faces, in fluid communication with the bearing cavity and allows lubricant to flow from the bearing cavity to the sealing surfaces.
The seal faces may include opposing non-engageable surfaces. At least one of the faces may include a stepped geometry. At least one of the sealing surfaces may include a beveled inner edge adjacent to the non-engageable surface. The generally wear-resistant material may include a tungsten carbide coating.
If desired, the sealing surfaces may be designed not to substantially migrate across the faces throughout the life of the rolling cutter rock bit under normal operating conditions. The gap may, if desired, be formed with a width of between approximately 0.005 inches and 0.010 inches.
Various embodiments of the present invention include a seal arrangement that has two rigid rings disposed between the leg of the bit body and the rolling cutter, the rigid rings having inner adjacent sides in fluid communication with the bit""s bearing cavity. The rings have opposing faces, which have opposing sealing surfaces. Each sealing surface occupies a portion of its respective face, includes wear resistant material and is generally non-migrating across its respective face. A gap is formed between a portion of the faces, extends from the inner side of each ring to the sealing surfaces of faces and allows lubrication to flow to the sealing surfaces from the bearing cavity.
In some embodiments of the invention, the seal arrangement includes first and second rigid rings positionable between the leg of the bit body and the rolling cutter, each ring having a first side in fluid communication with the bit""s bearing cavity when the seal arrangement is assembled within a rolling cutter rock drill bit. The rigid rings have opposing sealing faces, which include opposing seal interface surfaces that have a wear resistant coating. A distinct gap is formed between the sealing faces when the seal arrangement is assembled within the bit, the gap extending from the seal interface surfaces to the first side of each rigid ring.
The present invention also includes embodiments having two rigid rings disposed between the leg of the bit body and the rolling cutter, each rigid ring having a first side in fluid communication with the bearing cavity of a bit. The rigid rings have opposing faces, the faces having opposing seal interface surfaces. Each seal interface surface includes a wear resistant coating. The face of at least one of the rigid rings also has a non-engageable surface disposed adjacent to the first side of the ring, the non-engageable surface being non-engageable with the face of the other rigid ring and forming a gap between the faces. The gap allows the flow of lubricant to the first and second seal interface surfaces.